The motion of an object can be represented by motion graphs.
Common motion graphs include displacement-time graph, velocity-time graph and
acceleration-time graph.

Fig. 5-1

Displacement-time graph

A displacement-time graph shows the positions of a moving object
at different times. Fig. 5-1 shows the displacement-time graph of a car. From
time
to ,
the car moves forwards, and at
it has a displacement of 60 m. Then it remains stationary there for 5 s, and
finally moves back to its starting position in another 5 s.

The velocity of motion can be determined from the slope of the
displacement-time graph. The velocity of the car is
from
to ,
it is zero (the car is at rest) from
to
and is
from
to .
The negative slope in the last 5 s indicates that the car is moving backwards.
Note that the slope of the graph in each of the time intervals is a constant,
showing that the car is in a uniform motion (constant velocity) in each interval.

A boy walks at a velocity of
along a street for 50 s, suddenly he remembers that he has to buy something
in a shop that he has passed by, so he turns around and walks at a velocity of
for 10 s. He then stops for 30 s at the shop, and finally walks forward again
at
for another 20 s. Plot a displacement-time graph for the motion of the boy.